1. Field of the Invention
This invention relates to improvements in optical imaging composition apparatus, and especially to improvements in optical composing stages having a variable-area aperture for masking undesired portions of objects during the preparation of images by means of multiple exposures thereof.
2. Description of the Prior Art
The creation of composite images of objects using multiple exposure techniques is well-known. An important application of such technology is in the production of multi-colored images from black/white transparencies. Optical slides and prints, for example, can be produced by successive exposures of a suitable optical recording medium (i.e. color film or photosensitive paper) by sequentially imaging selected portions of originals illuminated by different colored light. Effective information presentation displays can be produced in this manner, such as bar charts, line graphs, pie charts, columnar charts and other special effects.
In a typical arrangement for the production of colored slides from black/white negatives, an optical composing stage is employed which has a variable-area aperture for successively presenting selected portions of the negative for imaging by transmission therethrough of diffused light from an illuminating light source onto the color slide film. For example, a 35 mm black/white negative is mounted by means of registration pins which engage the negative sprocket holes at an object plane in the housing of the stage. The housing has a window for directing light incident from an illuminating light source through the mounted negative for imaging by means of an adjacently positioned camera onto a photosensitive color film. A color-programmable, optical light filtering apparatus such as a "SLIDELIGHT" light box commercially available from Spectrum Studios, Hackensack, N.J., is used to provide an illuminating light source to give the desired light color hue, density and intensity. A plurality of movable blades positioned near the stage object plane, provides a variable-area aperture by which the negative can be suitably masked to present a selected portion of the negative for imaging by transmission therethrough of light of the selected color characteristics.
The process from art work to 35 mm black/white negative to multicolored display slide is relatively easy using an optical composing stage of a type to which the present invention finds application. For a typical word slide, a black/white 35 mm negative is prepared by photographing the prepared art work. The resulting black/white negative is positioned within the window of the optical composing stage by means of the registration pins. The blades of the variable-area aperture are then adjusted to reveal the first of the specific areas of the negative required for coloring. The desired color is set on the light box and transmitted through the unmasked portion of the negative as a first exposure of a frame of slide film located in a camera above the stage. The variable-area aperture is then adjusted to reveal the next selected portion of the black/white negative (or a selected portion of another negative) to colored light selected at the light box, and exposure proceeds in a similar way until the slide is completely exposed to provide a composite of the successively presented selected portions of the object negative (or negatives).
One problem encountered in the use of conventional optical composing stage is so-called "flaring" in the imaging of a presented portion of the object transparency due to the reflection and dispersion of light incident from the illuminating source onto the leading edges of the variable-area aperture-defining blades. The flaring manifests itself in the form of a fringed outline of the aperture setting of each selected object portion. The movable blades which define the aperture size are typically configured as two pairs of parallel opposed blades disposed at right angles. The composite image is thus compiled by imaging selected rectangular portions of the object transparency (or transparencies); and flaring takes the form of rectangular outlines surrounding different parts of the composite image. Such flaring distracts from the aesthetic appearance of the composite image and is thus undesirable.
Attempts have been made to minimize the flaring due to light reflections from the leading edges of the blades by reducing their thickness. Nevertheless, with the high resolution, long tonality and color high fidelity films usable for slide preparation today, even at blade thicknesses on the order of 0.006 inches or less (achievable by using thin film materials for blades), unacceptable flaring is still present.
Another problem confronting composite image construction using conventional optical stages is the achievement of good alignment between the position of horizontal and vertical linear characters or patterns on an object transparency and the sides of the rectangular opening of the variable-area aperture. For conventional stages, misalignment of the horizontal and vertical lines of the object transparency and the edges of the variable aperture is corrected by repositioning, i.e. rotating, the transparency in its mounted position on the stage, e.g. moving the alignment of the sprocket holes of a 35 mm black/white negative relative to the stage registration pins. This procedure is inaccurate, cumbersome and time-consuming and may require breaking the sprocket holes. Thus, a need exists for convenient rapid realignment of the transparency relative to the variable-area aperture.
Furthermore, though special effects are possible using conventional optical composing stages having a single object plane at which to mount a transparency, or at which to mount a plurality of immediately adjacent transparencies, the additional flexibility for special effects which would be offered by a plurality of spaced object planes in a single composing stage (wherein, e.g. one transparency could be in focus while a second transparency is out of focus) is not available.